Fig. 15. Magnification need for letter chart acuity and reading acuity. The chart compares the magnification need found for letter chart testing (1/V) with the magnification need for continuous text reading (M × D) for 150 consecutive low-vision patients. The numbers indicate the number of patients in each cell. For most patients, the two values are the same or differ by only one line interval (gray diagonal band). For a number of patients, the magnification need for continuous text is somewhat greater; this is known as the magnification reserve needed for reading fluency. For a few patients, the magnification need for continuous text was significantly greater (isolated gray cells). These patients represent exceptional cases; for most of them, letter acuity was obtained in a small island surrounded by scotoma, while reading acuity used a larger, more eccentric area, requiring more magnification.